Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		3 Months Ended	6 Months Ended
	Apr. 30, 2013	Feb. 29, 2012	Jun. 30, 2015	Jun. 30, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Gross proceeds in concurrent private placements		$ 12.0
Warrants to purchase common stock, exercise price		$ 20.00
Warrant contractual term		10 years
Purchase of warrant common stock		150,000
Warrants outstanding to purchase common stock			150,000	150,000	150,000
Weighted-average exercise price			$ 20.00	$ 20.00	$ 20.00
Warrant to purchase common stock were exercised			0	0
Series B Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Warrant common stock exercise price		$ 5.20
Purchase of warrant common stock		159,500
Follow-On Public Offering [Member]
Class of Stock [Line Items]
Issuance of common stock	5,750,000
Common stock offering price per share	$ 12.00
Net proceeds after underwriting discounts, commissions and offering expenses	$ 64.4
IPO [Member]
Class of Stock [Line Items]
Issuance of common stock		5,175,000
Net proceeds after underwriting discounts, commissions and offering expenses		$ 45.0
Conversion of outstanding preferred stock to common stock		24,332,186
Private Placement [Member]
Class of Stock [Line Items]
Issuance of common stock		1,200,000
Common stock offering price per share		$ 10.00